Want to ask a question - i had a few issues with brakepads a while back whereby the garage couldn't get the wheel (front) to turn on fitting the new pads (i.e. too tight). I thus pulled the calipers off & was aiming to apply a repair kit; on further inspection the pistons (ceramic) look fine, as to the rings / seals etc (although difficult to really tell).

i. The bike has 36k on it & to be honest i'm not convinced they would ever have been changed or rebuilt - despite their good condition, should i replace? Also it doesn't appear that you can just get the rings/seals for front calipers
ii. The pin's look semi-worn - should i replace? I was advised this by the garage who i took it too.

yep , id be changing the seals , cant do any harm ,
brakes are important and a seal kits cheap , before doing that though , crack both bleed nipples and check the wheel for rotation , incase its a master cyl problem ,,,,

Guys, no-one has responded to my query re just wanting to replace the seals as opposed to having replace pistons as well; on further investigation i'm still yet to find a provider who sells just the seals... Anyone know anyone who does this?

@ tanneman - yes i still have original hoses on the bike & i'm guessing you are about to recommend replace these as well? I can do if you strongly advise, but i was hoping to keep costs down (but i might already have noted, i'm not prepared to cut-corners when it comes to brakes but at some time want to not get carried away). If you do recommend, is there really a good argument to go with a braided pair (i've always wondered if this is more a boy-racer mentality or can you actually feel the difference to a standard pair)?

Brad, you will definitely notice a difference if you fit braided hoses, if your bike is getting on a bit you will probably be able to see the hoses you have now expand if you squeeze the lever hard, not what you want.
If you do replace them the best option is to go for twin lines from the master cylinder down to each caliper and lose the cross over pipe, its cheaper and a lot less bother. I have longer hoses on mine as I have the bars above the top yoke but I am sure somebody can tell you the standard lengths. I got mine from bikesnbits in Northern Ireland off ebay about £50 delivered I think. I can do you a nice line in Aircraft spec "P" clips if you need any.

Here is your problem. I had the same with the front and now with the rear which warped the disc. The brake lines is now so flexible that it cannot return all the fluid to the master cylinder. The return at the master closes and the flex in the hose is enough to put a bit of pressure on the remaining fluid which in turn prevents the callipers from returning to fully retracted position. The rear managed to to warp the disc on last years trip to Garmish. It is really bad.

The solution for the front was a new set custom made to be 2 hoses (black of course as to not advertise the upgrade) that fits onto 1 union at the master. This bleeds more easily than the original set. Don't throw away the original set if you go down this way. You may also opt just to have the flexible hoses replaced with braided ones and keep the link pipe at the lower brace. Take care when removing this because the metal is soft and not a lot of area for the tool to grab.

The symptoms usually feels as if the brakes are binding ever so slightly on the disc. You can force the pads off the disc but at first application of the brakes they return to previous position. I noticed the end of the brake lines at a track day, braking from high speed the lever came back to the bar and the brake force wasn't there any more. This was not brake fade as the Brembos are up to the job and the bike is non-ABS. It just happened suddenly and it remained like that all day. In the pits I had a quick look at it and you could see the lines bulging. After the braided hoses went on the brakes has been transformed. The tyres now have a real job on their hands to get the force to the tarmac but now the brake callipers don't feel up to the job of the improved brake lines. Another E500 for some Italian exotica to convert the system to radial brakes. But before spending such money on something you wouldn't notice on the road it is better to have the suspension set up and overhauled.

I can add that I do give the brakes attention over the year and they get cleaned quite often, not that I ride it in winter. The pistons and callipers are in good condition but if you are less anal with the maintenance then it would make sense to rebuild the callipers once in a lifetime. If it needs it do it, if in doubt do it. Try motorworks, james sherlock or your local. You need to know reg plate and what is written on the brake callipers (BMW or Brembo).

Possibly I'm misunderstanding what was meant, but the bit about the master cyl closing off on return? It closes off from the res upon application of lever and opens return to res (therefore to atmospheric pressure) upon release of the lever. Or it should, unless there's a problem, as was mentioned higher up the thread.

Admittedly the hole it has to go through is very small.

Edit: it does open up the wider topic of what it actually is that returns the fluid. Returns it back to atmospheric. Well the first thing is, it gets opened up to atmospheric!

I don't think any fluid returns. You release the pressure and the pads release the grip on the disk. No pressure no braking effect although the pads will probably be in contact with the disk to some small degree........
Maybe

bfisher wrote:Guys, no-one has responded to my query re just wanting to replace the seals as opposed to having replace pistons as well; on further investigation i'm still yet to find a provider who sells just the seals... Anyone know anyone who does this?

I kind of did answer this. If you pop the pistons out and see that they are not marked pitted and corroded there is no need to change them. What can also happen is the caliper itself corrodes where the seals run. This nips everything up and stops the piston retracting that few thousands of an inch.So if you dismantle your calipers all answers will be revealed.Brad

Merecat wrote:I don't think any fluid returns. You release the pressure and the pads release the grip on the disk. No pressure no braking effect although the pads will probably be in contact with the disk to some small degree........Maybe

What would happen, even in the short term, if the hole was blocked? If no flow into or out of the reservoir occurs, then we don't need the hole.